Exercise Device for Exercising Core Muscles

ABSTRACT

An exercise device includes a base frame and a carriage. The base frame includes at least one curved track having a first end and a second end. The second end is elevated above the first end. The carriage is moveable between the first end and the second end of the curved track. The carriage includes a support frame having an axis of rotation, an upper body frame coupled to the support frame and rotatable about the axis of rotation and a resistance mechanism coupled to the upper body frame to resist pivoting of the upper body frame about the axis of rotation.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is based on and claims the benefit of U.S. provisional patent application Ser. No. 60/825,209, filed Sep. 11, 2006, the content of which is hereby incorporated by reference in its entirety.

BACKGROUND

Core muscles of a human body include abdominal muscles, pelvic muscles and lower back muscles. Basically, a core muscle is any muscle located between the pelvis and the base of the ribcage. Core muscles are able to work together to support the spine. When a person strengthens their core muscles, a gain in balance and stability are realized.

Currently there are a wide-variety of exercises available to exercise core muscles. Some such exercises include conventional weightlifting using free weights, weight machines, bar bells and exercise “bands.” The free weights and barbells of a conventional construction include weighted ends and a hand held bar in the center. Oftentimes weight machines use pulley structures and hydraulic or pneumatic cylinders to aid a user in lifting weights in various positions. These machines also provide variable resistance to the user. Such exercise equipment can be intimidating to a novice and can also exert excessive stress or strain on the body, especially where the user does not have a great deal of experience in the particular type of weight training or weightlifting being used.

One type of exercising device includes a stack of weighted plates connected to a pulley structure and a connecting seat. An individual sits in the seat of the exercising device and pulls on the straps connected to the pulley structures as they bend at the waist. This type of machine exercises abdominal muscles. Although this exercising device is beneficial to the body, there are many disadvantages. In particular, this large piece of equipment is only designed to exercise one particular group of muscles in the abdomen. Furthermore, undue strain can be exerted on the spine.

Many exercises for exercising core muscles can also be performed without the use of weights or weighted machines. For example, stomach crunches can be performed while on the ground in a laying position. However, some users have difficulty getting into a laying down position to perform these stomach crunches.

The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.

SUMMARY

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.

An exercise device includes a base frame and a carriage. The base frame includes at least one curved track having a first end and a second end. The second end is elevated above the first end. The carriage is moveable between the first end and the second end of the curved track. The carriage includes a support frame having an axis of rotation, an upper body frame coupled to the support frame and rotatable about the axis of rotation and a resistance mechanism coupled to the upper body frame to resist pivoting of the upper body frame about the axis of rotation.

Many variations of exercises can be performed with the exercise device as described. Exercises can be performed that incorporate simultaneous use of the at least one curved track with rotation of the upper body frame about the axis of rotation. However, other exercises can be performed that incorporate just the rotation of the upper body frame about the axis of rotation or just the movement along the at least one curved track.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a front perspective view of an exercise device under one embodiment.

FIG. 2 illustrates back perspective view of the exercise device of FIG. 1.

FIG. 3 illustrates a partial enlarged view of a resistance mechanism under one embodiment.

FIG. 4 illustrates a side view of the exercise device illustrated in FIG. 1.

FIG. 5 illustrates a side view of the exercise device of FIG. 1 including a use at a first elevation.

FIG. 6 illustrates a side view of the exercise device of FIG. 1 at a second elevation.

FIG. 7 illustrates a front perspective view of an exercise device under one embodiment.

FIG. 8 illustrates a perspective view of the exercise device of FIG. 7 in a stored position.

FIG. 9 illustrates a front perspective view of an exercise device under one embodiment.

DETAILED DESCRIPTION

FIG. 1 illustrates a front perspective view of an exercise device 100 under one embodiment. Exercise device 100 includes a base frame 102 and a carriage 104. Base frame 102 includes a pair of curved tracks 106, a support leg 108 and a foot rest 109. Although exercise device 100 includes a pair of curved tracks 106, exercise device 100 can have any number of tracks including a single track. Curved tracks 106 include first ends 110 and second ends 112. First ends 110 are proximate to the ground or in contact with the ground, while second ends 112 are elevated above first ends 110 by support leg 108. First ends 110 are also coupled to foot rest 109, which is oriented at an angle from curved tracks 106. Curved tracks 106 extend from first ends 110 to second ends 112 along a radius of curvature. Although curved tracks 106 are illustrated as rails having a rectangular cross-section, curved tracks can have any type of geometrical shaped cross-section.

Carriage 104 includes a seat 114 coupled to curved tracks 106 by rollers 116. Rollers 116 are configured to follow curved tracks 106 back and forth between first ends 110 and second ends 112 as illustrated by arrow 118. Gravitational force causes a user to use a greater level of intensity to move carriage 104 towards second ends 112 versus first ends 110. Also, it takes a greater level of intensity to move carriage 104 towards second ends 112 on the curved shape of tracks 106 versus tracks that are straight.

Although not specifically illustrated in FIG. 1, rollers 116 can be restricted to move along only certain portions of curved tracks 106 with a restriction mechanism. In addition, although FIG. 1 illustrates exercise device 100 having rollers 116 to move back and forth between first ends 110 and second ends 112, it should be understood that other types of mechanisms can be used. For example, exercise device 100 can include bearings or other devices for sliding along curved tracks 106. Furthermore, coupled to seat 114 includes a pair of lower body pads 120. Lower body pads 120 prevent a user from sliding off of seat 114 when carriage 104 is moving towards second ends 112.

Carriage 104 also includes a support frame 122, an upper body frame 124 and a resistance mechanism 126. Support frame 122 includes a pair of bars 128 fixed to seat 114. Support frame 122 also includes an axis of rotation 130 as indicated by dashed lines. Upper body frame 124 is coupled to support frame 122 and is rotatable about the axis of rotation 130. Upper body frame 124 is rotatable about the axis of rotation 130 in a first direction 129 towards first ends 110 of curved tracks 106 as well in a second direction 131 towards second ends 112 of curved tracks 106. Upper body frame 124 includes a pair of bars 132 coupled together by a cross bar 133. Attached to each bar 132 includes a handle 134. Handles 134 are oriented in an upward direction as illustrated. Cross bar 133 includes an upper body pad 135. Cross bar 133 can be positioned behind a user such that a back of the user is resting against upper body pad 135 or cross bar 133 can be positioned in front of a user such that a chest of the user can rest against upper body pad 135. When cross bar 133 is positioned behind a user, a user can place their hands on handles 134. When cross bar 133 is positioned in front of a user, a user can place their arms, elbows and/or hands around cross bar 133. Resistance mechanism 126 is coupled to support frame 122 and upper body frame 124. Resistance mechanism includes an upper bar 136 attached to upper body frame 124 and a lower bar 138 attached to support frame 122. Resistance mechanism 126 is better illustrated in FIGS. 2 and 4.

FIG. 2 illustrates a back perspective view of exercise device 100 illustrated in FIG. 1. As illustrated, resistance mechanism 126 includes upper bar 136 attached to upper body frame 124, lower bar 138 attached to support frame 122 and a biasing device 140. In particular, lower bar 138 is attached to one of the bars 128. In one embodiment, upper bar 136 is a curved bar as illustrated in FIGS. 1 and 2. However, in some embodiments, upper bar 136 can be straight. Upper bar 136 includes a first end 140 and a second end 142. Upper bar 136 also includes a plurality of first end apertures 144, a plurality of second end apertures 146 and a center aperture 148 located between first end 140 and second end 142. First end apertures 144 are located in series between first end 140 and center aperture 148, while second end apertures 146 are located in series between second end 142 and center aperture 148.

As illustrated in FIG. 2, first end apertures 144, second end apertures 146 and center aperture 148 can be formed through upper bar 136 from an outwardly facing side of exercise device 100 to an inwardly facing side of exercise device 100. However, as illustrated in the FIG. 3 alternative embodiment, resistance mechanism 226 can include an upper bar 236 having first end apertures 244, second end apertures 246 and a center aperture (hidden from view) that are formed through upper bar 236 from an upwardly facing surface to a downwardly facing surface. In addition, other alternative formations of apertures can be used. In the FIG. 3 embodiment, resistance mechanism 326 includes a handle 247. Handle 247 is coupled to a pin (hidden from view). To detach the pin from an aperture, a user can pull up on the handle in the direction as illustrated for ease of adjustment to a new aperture.

Referring back to FIG. 2, in one embodiment lower bar 138 is a curved bar as illustrated in FIGS. 1 and 2. However, in some embodiments, lower bar 138 can be straight. Lower bar 138 includes a first end 150 and a second end 152. Lower bar 138 also includes a first end aperture 154 and a second end aperture (hidden from view). First end aperture 154 is located in close proximity to first end 150 and second end aperture is located opposite from first end aperture 154 in close proximity to second end 152. While FIG. 2 illustrates first end aperture 154 and the second end aperture as being formed from an outwardly facing side to an inwardly facing side, it should be recognized that first end aperture 154 and the second end aperture can be formed in alternative ways. For example, first end aperture 154 and the second end aperture can be formed from a downwardly facing surface to an upwardly facing surface like the alternative embodiment of upper bar 236 illustrated in FIG. 3.

Biasing device 140 is selectively attached to upper bar 136 at a rod end 156 through one of the first end apertures 144, one of the second end apertures 146 or center aperture 148. Biasing device 140 is selectively attached to lower bar 138 at a piston end 158 through one of first end aperture 154 or the second end aperture. As illustrated in FIG. 2, biasing device 140 can be a gas compression spring, such as a nitrogen gas spring.

Lower bar 138 is responsible for allowing a selection of a direction of resistance as well as a selection of a neutral start position of upper body frame 124, while upper bar 136 is responsible for allowing a selection of an amount of resistance based on the selected direction of resistance. By resistance mechanism 126 having adjustable or variable resistance, either the intensity of a user's workout is increased or aid in assisting the user to perform exercises is increased depending on the type of exercise. In addition, depending on the type of exercise, the greater the resistance the more aid in assisting the user to perform an exercise.

With piston end 158 attached to lower bar 138 through the second end aperture and rod end 156 attached to one of the second end apertures 146, upper body frame 124 resists rotation about the axis of rotation 130 in second direction 131 (also illustrated in FIG. 1), which is towards second ends 112 of curved tracks 106. In addition, upper body frame 124 is biased into a first neutral start position and is prevented from rotating about the axis of rotation 130 in first direction 129, which is towards first ends 110 of curved tracks 106.

Solid lines in the side view illustrated in FIG. 4 of exercise device 100 illustrate first neutral position 160. It should be realized that whenever piston end 158 is attached to the second end aperture of lower bar 138, rod end 156 needs to be attached to any one of the second end apertures 146 or to central aperture 148. If rod end 156 is attached to central aperture 148, then no added resistance is added to the rotation about the axis of rotation 130 in second direction 131. If rod end 156 is attached to one of the second end apertures 146, then some amount of resistance is added to the rotation about the axis of rotation 130. In particular, less resistance is added to the rotation about the axis of rotation 130 the further rod end 156 is attached to one of the second end apertures 146 that is located towards central aperture 148. More resistance is added to the rotation about the axis of rotation 130 the further rod end 156 is attached to one of the second end apertures 146 that is located towards second end 142.

With piston end 158 attached to lower bar 138 through first end aperture 154, upper body frame 124 resists rotation about the axis of rotation 130 in first direction 129 (also illustrated in FIG. 1), which is towards first ends 110 of curved tracks 106. In addition, upper body frame 124 is biased into a second neutral start position and is prevented from rotating about the axis of rotation 130 in second direction 131, which is towards second ends 112 of curved tracks 106.

Dashed lines in the side view illustrated in FIG. 4 of exercise device 100 illustrate second neutral position 162. It should be realized that whenever piston end 158 is attached to first end aperture 154 of lower bar 138, rod end 156 needs to be attached to any one of the first end apertures 144 or to central aperture 148. If rod end 156 is attached to central aperture 148, then no added resistance is added to the rotation about the axis of rotation 130 in first direction 129. If rod end 156 is attached to one of the first end apertures 144, then some amount of resistance is added to the rotation about the axis of rotation 130. In particular, less resistance is added to the rotation about the axis of rotation 130 the further rod end 156 is attached to one of the first end apertures 144 that is located towards central aperture 148. More resistance is added to the rotation about the axis of rotation 130 the further rod end 156 is attached to one of the first end apertures 144 that is located towards first end 140. Exercises that can be performed from the first neutral position 160 and the second neutral position 162 shown in FIG. 4 ill be discussed in detail below.

FIG. 5 illustrates a side view of the exercise device 100 of FIG. 1 including a user 164 at a first elevation 166. As previously discussed, first ends 110 of curved tracks 106 are proximate to the ground or in contact with the ground, while second ends 112 of curved tracks 106 are elevated above first ends 110 by support leg 108. It is noted that the greater amount of elevational difference between first ends 110 and second ends 112 corresponds with a greater level of intensity while using exercise device 100. Therefore, support leg 108 includes a fixed member 167 and a telescoping member 168 as illustrated in FIG. 6. Telescoping member 168 is slidable within fixed member 167 and selectively adjustable to change to various different elevations. As illustrated in FIG. 6, a second elevation 169 is illustrated.

FIG. 7 illustrates a front perspective view of an exercise device 300 under one embodiment. Exercise device 300 is similar to exercise device 100 in that it includes a base frame 302 and a carriage 304. Also similar to exercise device 100, base frame 302 includes a pair of curved tracks 306, a support leg 308 and a foot rest 309. Curved tracks 306 include first ends 310 and second ends 312. First ends 310 are proximate to the ground or in contact with the ground, while second ends 312 are elevated above first ends 310 by support leg 308. First ends 310 are also coupled to foot rest 309, which is oriented at an angle from curved tracks 306.

Carriage 304 includes a seat 314 coupled to curved tracks 306 by rollers 316. Seat 314 includes a curved back rest to prevent a user from sliding off of seat 314 when carriage 304 is moving towards second ends 312. Rollers 316 are configured to follow curved tracks 306 back and forth between first ends 310 and second ends 312 as illustrated by arrow 318. Carriage 104 of exercise device 100 includes rollers 116 that follow an outer surface of curved tracks 106. Carriage 304 of exercise device 300, however, includes roller 316 that follow an inner channel 370 of curved tracks 306.

Like exercise device 100, carriage 304 also includes a support frame 322, an upper body frame 324 and a resistance mechanism 326. Support frame 322 includes a pair of bars 328 fixed to seat 314. Support frame 322 also includes an axis of rotation 330 as indicated by dashed lines. Upper body frame 324 is coupled to support frame 322 and is rotatable about the axis of rotation 330. Upper body frame 324 is rotatable about the axis of rotation 330 in a first direction 329 towards first ends 310 of curved tracks 306 as well in a second direction 331 towards second ends 312 of curved tracks 306. Upper body frame 324 includes a pair of bars 332 coupled together by a cross bar 333. Attached to each bar 332 includes a handle 334. Handles 134 are positioned in proximity to a user's head. Cross bar 333 includes an upper body pad 335. Cross bar 333 can be positioned behind a user such that a back of the user is resting against upper body pad 335 or cross bar 333 can be positioned in front of a user such that a chest of the user can rest against upper body pad 335. When cross bar 333 is positioned behind a user, a user can place their hands on handles 334. When cross bar 333 is positioned in front of a user, a user can place their arms, elbows and/or hands around cross bar 333. Resistance mechanism 326 is coupled to support frame 322 and upper body frame 324.

Resistance mechanism 326 is configured to bias upper body frame 324 into a neutral position. Resistance mechanism 326 is able to adjust the position of the neutral position. In addition, resistance mechanism 326 resists rotation about the axis of rotation 330 in first direction 329, which is towards second first end 310 of curved tracks 306, as well as second direction 331, which is towards second ends 312 of curved tracks 306.

To accomplish these features, resistance mechanism includes a plate 372 configured to house a spring (hidden from view) coupled to upper body frame 324 and to support frame 322. For example, the spring can be a torsion spring. Plate 372 includes a first slot 374 and a second slot 376. When first slot 374 of plate 372 is inserted into a pin 378 attached to upper body frame 324, upper body frame is in a first neutral position. When second slot 376 of body 372 is inserted into pin 378 attached to upper body frame 324, upper body frame 324 is in a second neutral position. Plate 372, although not illustrated, can include a plurality of slots for changing the neutral position of upper body frame 324. Resistance mechanism 326 can be an adjustable or variable resistance mechanism. To add resistance or assistance, a plurality of plates 372 can be added to exercise device 300. Each plate 372 includes first and second slots and a spring. The more plates added to exercise device 300, the more resistance is added to resist upper body frame 324 from rotating about the axis of rotation 330.

FIG. 8 is a perspective view illustrating exercise device 300 in a collapsed or folded state. To collapse exercise device 300 into a smaller size for shipping or storage, support leg 308 is folded, upper body frame 324 is collapsed and foot rest 309 is folded inwardly.

FIG. 9 illustrates a front perspective view of an exercise device 400 under one embodiment. Exercise device 400 is similar to exercise device 300 of FIG. 3. However, instead of first ends 410 of curved tracks 406 being coupled to foot rest 309, first ends 410 are spaced apart from foot rest 409. Such an embodiment makes curved tracks 406 shorter. Shorter curved tracks 406 allow exercise device 400 to have a smaller shipping package.

Referring back to FIG. 5 illustrating a user 164 using exercise device 100, it is demonstrated that many different exercises can be performed such that various core muscles including abdominals, pelvic muscles, lower back muscles and other muscles including buttocks, gluteus and thighs. User 164 is positioned on seat 114 with his/her legs extended and their feet planted on foot rest 109. In FIG. 5, the user's back is resting on upper body pad 135. However, although not illustrated, cross bar 133 can be positioned in front of user 164 such that a chest of the user can rest against upper body pad 135. When cross bar 133 is positioned behind a user, a user can place their hands on handles 134 as illustrated in FIG. 5. When cross bar 133 is positioned in front of user 164, the user can place their arms, elbows and/or hands around cross bar 133.

In one variation, piston end 158 can be placed in first end aperture 154 of lower bar 138 while rod end 156 can be placed in one of the first end apertures 144 of upper bar 136. In this resistance mechanism position, user 164 grabs handles 134 or upper body pad 135 (depending on whether cross bar 133 is in front of user 164 or behind user 164) and extends their legs to force carriage 104 towards second ends 112 of curved track 106 while simultaneously rotating upper body frame 124 about the axis of rotation 130 towards first ends 110 of curved track 106 to perform an abdominal crunch. In another embodiment of the same resistance mechanism position, user 164 can start in an extend leg position and then rotate upper body frame 124 about the axis of rotation 130 towards first ends 110 while simultaneously bending their knees to make seat 114 slide towards first ends 110 to perform an abdominal compression. User 164 can then extend their legs to move carriage 104 back up tracks 106 while extending their back backwards.

In another variation, user 164 can perform the same motion as described above on the same resistance mechanism position. However, user 164 positions their body on seat 114 at an angle such that the oblique abdominal muscles can be targeted.

In yet another variation, piston end 158 can be placed in the second end aperture of lower bar 138 while rod end 156 can be placed in one of the second end apertures 146 of upper bar 136. In this resistance mechanism position, user 164 grabs handles 134 or upper body pad 135. In this variation, user 164 can stabilize their lower body and perform back extensions by moving upper body frame 124 towards second ends 112 of curved tracks 106 and returning to an upright position.

In still another variation, with piston end 158 in either first end aperture 154 or the second end aperture of lower bar 138, exercise device 100 can be elevated using telescoping member 168. In this position, user 164 places their hands on their thighs. The user 164 can place their hands on their thighs and extend and bend at the knees to perform a squat. Such an exercise move targets buttocks, hips and thigh muscles. This motion can be varied by using one leg at a time for a more intense workout.

Embodiments of the detailed description describe variations of a resistance mechanism 126, 226 and 326. It should be realized that resistance mechanism can be any type of mechanism that is biasing or otherwise that adds resistance or assistance to the rotation of an upper body frame about an axis of rotation. For example, a resistance mechanism can be as simple as a spring resistance, band resistance or weighted resistance.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. 

1. An exercise device comprising: a base frame including at least one curved track having a first end and a second end, the second end of the curved track elevated above the first end of the curved track; a carriage moveable between the first end and the second end of the curved track, the carriage comprising: a support frame having an axis of rotation; an upper body frame coupled to the support frame and rotatable about the axis of rotation; and a resistance mechanism coupled to the upper body frame to resist rotation of the upper body frame about the axis of rotation.
 2. The exercise device of claim 1, wherein the base frame comprises a support leg configured to elevate the second end of the curved track above the first end of the curved track.
 3. The exercise device of claim 2, wherein the support leg comprises a fixed member and a telescoping member, wherein the telescoping member is slidable within the fixed member and selectively adjust the elevation of the second end of the curved track above the first end of the curved track.
 4. The exercise device of claim 1, wherein the resistance mechanism is configured to bias the upper body frame towards one of a first and second neutral position and resist rotation of the upper body frame about the axis of rotation in one of a first direction and a second direction, wherein the first direction is towards the first end of the curved track and the second direction is towards the second end of the curved track.
 5. The exercise device of claim 4, wherein when the resistance mechanism resists rotation of the upper body frame about the axis of rotation in a first direction, the resistance mechanism prevent rotation about the axis of rotation in the second direction.
 6. The exercise device of claim 4, wherein when the resistance mechanism resists rotation of the upper body frame about the axis of rotation in a second direction, the resistance mechanism prevents rotation about the axis of rotation in the first direction.
 7. The exercise device of claim 1, wherein the resistance mechanism comprises at least one plate housing a spring mechanism that is couplable to the support frame and couplable to the upper body frame.
 8. The exercise device of claim 7, wherein the plate further comprises a plurality of apertures configured for receiving a pin attached to the upper body frame.
 9. The exercise device of claim 8, wherein the pin is configured to be selectively received in the one of the plurality of apertures, each aperture includes a provides the upper body frame to be placed in different neutral positions.
 10. The exercise machine of claim 7, wherein the resistance mechanism comprises a variable resistance mechanism by coupling a variable amount of plates to the support frame and to the upper body frame.
 8. The exercise machine of claim 4, wherein the resistance mechanism comprises a piston selectively couplable to positions along an upper bar attached to the upper body frame and selectively couplable to positions along a lower bar attached to the support frame, wherein the coupling the piston to the upper bar provides resistance to the upper body frame and coupling the piston to the lower bar changes
 11. The exercise device of claim 4, wherein the resistance mechanism comprises a piston that is couplable to a lower bar attached to the support frame and couplable to an upper bar attached to the upper body frame, the upper bar including a first end, a second end, a plurality of first end apertures and a plurality of second end apertures and the lower bar including a first end, a second end, a first end aperture and a second end aperture.
 12. The exercise device of claim 11, wherein the piston is couplable to the upper bar through the second end apertures and to the lower bar through the second end aperture to resist the upper body frame from rotating about the axis of rotation in the second direction and to prevent the upper body frame from rotating about the axis of rotation in the first direction.
 13. The exercise device of claim 11, wherein the plate is couplable to the upper bar through the first end apertures and to the lower bar through the first end aperture to resist the upper body frame from rotating about the axis of rotation in the first direction and to prevent the upper body frame from rotating about the axis of rotation in the second direction.
 14. The exercise machine of claim 11, wherein the plurality of first end apertures and the plurality of second end aperture provide resistance mechanism with selective variable resistance.
 15. The exercise device of claim 1, wherein the resistance mechanism provides variable resistance.
 16. A method of performing an exercise comprising: moving a carriage between a first end and a second end of at least one curved track, wherein the second end is elevated above the first end; and rotatably actuating an upper body frame coupled to the carriage about an axis of rotation, the upper body frame coupled to a resistance mechanism to resist rotation of the upper body frame about the axis of rotation.
 17. The method of claim 16, further comprising selectively adjusting a support leg supporting the elevation of the second end above the elevation of the first end.
 18. The method of claim 16, wherein rotatably actuating the upper body frame comprises rotatably actuating the upper body frame in one of a first direction and a second direction, wherein the first direction is towards the first ends of the curved track and the second direction is towards the second ends of the curved track.
 19. The method of claim 18, wherein resistance mechanism simultaneously resists rotation of the upper body frame about the axis of rotation in the first direction and prevents rotation of the upper body frame about the axis of rotation in the second direction.
 20. The method of claim 18, wherein resistance mechanism simultaneously resists rotation of the upper body frame about the axis of rotation in the second direction and prevents rotation of the upper body frame about the axis of rotation in the first direction. 